This invention relates to roll correction for a vehicle, and more particularly to a roll correction system which levels a vehicle during a turn-induced roll while compensating for countersteer.
The background of the invention includes vehicles, such as automobiles, which have a body, a plurality of wheels, and a suspension connecting the body to the wheels.
When such a vehicle turns, the suspension permits the vehicle body to rotate about its longitudinal axis in response to a rolling force exerted on the body during the turn. Typically, the vehicle's passengers experience this effect as the tilt of the vehicle body, with the side of the body on the outside of the curve being relatively lower than the side of the body on the inside or the curve. Conventionally, this is referred to as "roll".
The inventor has invented mechanisms, apparatuses, and systems for correcting roll of a vehicle body. See, for example, U.S. Pat. Nos. 5,161,822; 5,174,603; and, 5,219,181, all of which are incorporated herein by reference.
In the incorporated patents, roll compensation (or, "tilt correction", in the patents) is provided by a valved hydraulic signal generator that produces a hydraulic signal conditioned to indicate a vehicle roll direction. The hydraulic signal is differentially generated, and includes pressurizing and return components. Cylinder and piston assemblies are mounted for roll correction at the wheels of the vehicle. Typically, a hydraulic circuit connected to the valved hydraulic signal generator and to the cylinder and piston assemblies conducts the differential hydraulic signal to the cylinder and piston assemblies. The hydraulic signal moves the pistons in the cylinder and piston assemblies in complementary directions on either side of the vehicle. The directions of piston movement counteract roll and thereby level a vehicle body during a turn.
In the prior art, the condition of the hydraulic signal precisely indicates the direction in which the vehicle is being steered. In most cases, the steering direction is the same as the direction in which the vehicle is turning ("the turning direction"). Likewise, it will be appreciated that since the vehicle rolls to the outside of a turn, the roll direction will be known from the turning direction.
In the incorporated patents, the hydraulic signal is conditioned in response to a steering direction of the vehicle. For example, in the incorporated '822 patent, the hydraulic signal source includes a valve with a cylinder within which a piston is disposed for longitudinal sliding movement. The piston is connected by mechanical linkage to an automobile steering assembly and is moved in one longitudinal direction or another with respect to the cylinder when the steering assembly is operated to turn the vehicle. Accordingly, the position to which the piston is moved indicates a steering direction of the automobile. Ports are longitudinally distributed along, and open into, the cylinder. The position of the piston configures hydraulic flow between the ports so that pressure and return potentials are provided to operate the cylinder and piston assemblies in order to correct for roll.
While the effectiveness of the roll correction technology invented by the inventor and described and claimed in the incorporated patents has been widely acknowledged, to date no provision has been made to correct for countersteer as might occur, for example, when a vehicle begins to slide while turning. In such a case, the operator would instinctively reverse the direction of the steering wheel toward the outside of the turn in order to regain control of the vehicle. Since, in the prior art system of the '822 patent, the hydraulic signal essentially indicates the steering direction such a countersteer condition would result in reversal of the sense of the hydraulic signal since the centrifugal force of the sliding vehicle maintains the roll to the outside of the turning direction, countersteer would cause an undesirable reversal in roll correction by applying elevation to the side of the vehicle on the inside of the turn. Since the inside edge is already elevated by centrifugal force of the turn, such correction exaggerates the roll condition.
Further, the inventor has determined that roll correction is unnecessary and perhaps undesirable at low vehicle speeds. However, because of the mechanical linkage between the valved hydraulic signal generator described in the '822 patent and vehicle steering assembly, tilt correction is introduced at any speed including low speeds when the suspension acts to level the vehicle in a turn.
Accordingly, there is a manifest need to compensate countersteering in the prior art roll correction systems exemplified in the incorporated patents, and there is a further need to bypass or disable roll correction altogether at low vehicle speeds.